A switching power supply is high in power conversion efficiency, smaller in size and lighter in weight than a power capacity, and low in the costs, and therefore has been widely employed from a small-capacity power supply to a large-capacity power supply. There have been known switching power supplies such as an AC-DC converter that converts an AC power from an AC power supply into a DC power supply, a DC-DC converter that steps down or up a voltage of the DC power to obtain another DC power, and a DC-AC converter that converts the DC power into the AC power.
The switching power supply is required to meet an electro-magnetic compatibility (EMC). The switching power supply causes intense electro-magnetic interference (EMI) to be generated with the switching operation, and therefore may incur drawbacks such as malfunction or breakdown of another device as a noise generator source. Accordingly, noise suppression is strongly required.
For example, WO2009/123054 discloses a technology in which an asynchronous modulation processor and a pulse position modulator are disposed downstream of a pulse width modulation processor, the asynchronous modulation processor or the pulse position modulator is selected at random to diffuse a frequency spectrum of the noise. Also, Japanese Unexamined Patent Application Publication No. 2006-288103 discloses a method in which three different intervals are provided between the respective rising edges of drive pulses of a power switching element to diffuse a switching frequency.